1. Field of the Invention
The present invention relates to a method for determining, by means of an ultrasonic echograph, the compliance and the blood pressure of an artery containing flowing blood, according to an artery model.
The invention also relates to an ultrasonic echograph having a system for carrying out said method.
2. Description of Related Art
Such a method is already known from the publication entitled "The Static Elastic Properties of 45 Human Thoracic and 20 Abdominal Aortas in Vitro and the Parameters of the Model" by G. J. LANGEWOUTERS et alii, published in "J. Biotech.,17, 1984, pp. 425-435". Said document discloses an artery model based on the hypothesis of pure elastic behaviour of arterial walls. First, direct measurements are obtained from IN VITRO experimentations, in static pressure conditions, and a pressure/arterial diameter diagramm is constructed from the experimental measurements. Then, a relationship (3) between the arterial cross-section and the pressure is established. Said relationship (3) called model is calculated based on Young's modulus (3a) which increases with pressure according to a second order function. Algebraic manipulation then integration of said modulus, taking into account boundary conditions, yields said general formulation (3) of the arterial cross-section (A(p)) value as a parametrical function of pressure (p), which only takes into account pure elastic behaviour of the artery. The derivative of said general formulation (3) with respect to pressure provides a formulation (4) of the static compliance (C(p)) as a parametrical function of pressure (p.428, col.1,2). The direct measurements and the results obtained by calculations using the model of a purely elastic artery are compared.
According to the author of this publication (p.429, col.1), these formulations (3,4) are valid for homogeneous, isotropic, piece-wise linear, purely elastic material with cylindrical cross-section. Thus, application to aortas is a gross approximation.
Nowdays, diagnosis of vascular diseases and therapeutic choices have to be based on the analysis of the arterial lesion morphology and on the analysis of blood flows. These informations must be obtained with accuracy, and without using invasive means.